All legacy tools that have attachments should use the "new" file picker in place of the attachment widget. Calendar and Announcements are using the new file picker as of August 2. Other tools should be converted to it, using Calendar and/or Announcements as examples.
The new file picker allows the the tool invoking it to specify that the file picker should display all content collections the user has access to instead of just showing the resources in the current site. It would make sense for the tool to have an init-param with a value of "true" or "false" indicating whether the attachment widget (the file picker) should show all content collections the user has access to. This would be useful, for example, to a student who wants to attach a document from a course site to a Calendar in MyWorkspace (using the "true" setting) while still avoiding the case where users make attachments to a project site from another site that other users have no rights in.